Why do I cough up clear phglem/mucus?

I am a 23 year old white male. I am a full time student. I have had this problem for at least 3 years. I am an ex smoker, but did not smoke alot. I quit smoking 3 years ago. I also get sore throats occasionally. In addition to coughing up clear phglem/ mucus, I occasionally cough up dark green phglem. I am not taking any medications. I live in an area with slightly higher radon levels than normal.

Answer

First of all, congratulations on quitting smoking! This is probably the most important health decision you can make over the long term.
There are a few different possible causes of chronic cough and mucus production. Fortunately this is unlikely to be a serious problem, however as always if you experience concerning symptoms like weight loss, night sweats, or coughing up blood you should talk to your doctor immediately.
The most likely cause of your cough is allergic rhinitis (nasal allergies) or chronic sinus congestion. These are related conditions which are caused by irritation and inflammation of the lining of the nasal and sinus passages, usually related to contaminant particles in the air (smoke, dust, mold, mites). The inflammation causes dripping of mucus down the back of the throat, which causes the cough and mucus.
Fortunately, these conditions are easily treated, once the diagnosis has been confirmed by your primary care doctor. Irrigation of the nasal passage with saline solution, using the Nettipot or a similar system, is very effective. Similarly, some prescription medications, especially nasal steroid sprays, can be very helpful in reducing symptoms.
I suggest seeing your doctor first, as they will be able to help you decide which treatment is best for you.

This answer is for general informational purposes only and is not a substitute for professional medical advice.

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